Electron emitter



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INVENTOR.

Patented Feb. 7, 1939 UNITED STATES PATENT OFFICE ELECTRON EMIT'IEBl John C. Batchelor, New York, N. Y.

Application December 13, 1934, Serial No. 757,318

6 Claims.

My invention relates to an electron emitting cathode, and, more particularly, to such electron emitting cathodes as are used in cathode ray tubes and similar devices.

An object of my invention is to provide an in- D directly heated electron` emitting cathode so dis posed and mounted in conjunction with an electrode whose purpose is to control the number of electrons drawn from said cathode, that the spacing between the cathode and the control electrode may be more accurately fixed during manufacture than is possible with the mounting means in use prior to my invention.

A further object of my invention is to provide r such an electron emitting cathode so mounted with respect to its control element that the spacing between the cathodeand the control element is maintained substantially constant regardless of the temperature of the emitting cathode.

These and other objects will be readily apparent from the following description of my invention.

It has been customary in the past, in the construction of cathode ray tubes in which the intensity of the electron beam is to be' controlled i by means of a perforated disc. control element, to 2,5 use as an electron emitter an elongated cylindrical tube having one end closed by a metal disc or cap and further having a heating coil element in serted into the cylindrical tube at the open end for the purpose of heating the cylinder which in turn communicates heat to the flat closed end. On the closed end of the tube, which may be made of nickel or other suitable metal, is applied a coating of a material, such as a mixture of barium and strontium oxides, which is capable of i emitting electrons when heated. The cathode is then mounted rigidly to a support fastened at a point adjacent its open end in such a manner that when the cathode cylinder is heated. to a tem perature at which electrons will be emitted from its emitting surface, that emitting surface will by the expansion ofthe tube be caused to move in a direction away from the point of support of the cathode.

Thus it is apparent that when a control element comprising a perforated disc mounted in a cylinder is rigidly supported on a member mechanically in communication with the member which suppo-rts the cathode so that theemitting surface or" the cathode is adjacent the perforation in the control disc, the expansion oi the cathode upon being heated will cause the emitting surface to move nearer the perforation in the disc. In this manner an effect is introduced in the operation of 55 the tube which must be compensated for in the (Cl. Z50-162) construction of the tube while the cathode is cold l in order that the cathode to grid spacing will be of the value conducive to the proper operation of the tube when the cathode is heated. This compensation is further complicated by the fact that the range of temperatures over which the tube is often called upon to operate because of variations in the voltage supplying the heating element of the cathode, will cause a variation of the cathode to grid spacing with the applied Voltage, and consequently the best compensation which can be ap 0 plied is that :for a mean value of heater voltage.

A further disadvantage of this type of cathode mounting lies in the fact that, in the construction commonly used, it is diflicult accurately to establish the initial cathode to grid spacing because easy access to the grid-cathode region is made diicult by the extended cylindrical skirt which is required on the grid to provide certain electrostatic shielding which is required in the tube.

i rthermore, inasmuch as this spacing is often 20 only a few thousandths oi an inch, a variation of the order of a thousandth. of an inch represents an error of several percent.

With the foregoing in mind I have provided a new type oi cathode mounting for use in cathode 25 ray tubes such that the length of the spacing between the cathode and the grid maybe properly established when the tube is constructed. Further, the length of that spacing will be substantially independent of the temperature at which 310 the cathode is operated. l

In order to understand the explanation of my invention, it is convenient to refer to the draw'- ing of which Figure 1 represents an enlarged sectional view of one form of my invention; Fig- 35 ure 2 is an enlarged sectional view of a modied insulating member for establishing the spacing;

Figure 3 represents an enlargedsectio-nal View or another form of my invention; Figure 4 shows an enlarged sectional vie-w of a still further form 40 of my invention.

` Referring to Figure 1,-a cylindrical metal tube l, which may be of nickel, tantalum or other suitable metal, has attached to its upper end a disc-like metal member 2, of nickel, platinum or other metal, on the outer surface of which is applied a film 3 of material capable of emitting electrons. Inserted in the tube l is a heating element 4 consisting preferably of a bilaterally wound coil of tungsten wire suitably insulated by refractory oxides and having its end-terminals 5 welded to the lead-in wires 6. Y Mounted on the support wires 'l coaxially with the emitting disc 2 is a control elementcompris- 55 ing a cylindrical metal member 8 containing the perforated disc 9 and so disposed that the aperture I in the disc 9 lies substantially parallel to and adjacent the emitter coating 3. Serving as a spacing member and mounted between the emitter disc 2 and the perforated disc 9 is the insulating ring II. The ring II and the disc 2 are maintained in a position coaxial with the aperture I0 by the fianged centering ring I2 welded or otherwise fastened to the perforated disc 9 and fitting closely to the ring I I.

Near the lower extremity of the cathode tube I is a pair of lugs I3 to which is fastened a pair of spring members I4. The opposite ends of the spring members I4 are welded or otherwise fastened to the support wires I5 in a manner such that the tension on the spring members I4 will cause a compressing force to be exerted upon the portion of the ring II which lies between the emitter disc 2 and the perforated disc 9.

In operation, a voltage is applied between the portions of the lead-in wires 6 which extend outside of the vacuum tube in which my improved cathode is mounted such that the temperature of the heating element 4 is sufficiently increased to heat by radiation the cathode tube I which in turn heats by conduction the emitter disc 2 and its emitter coating 3. Under the influence of the elevated temperature the cathode tube I will be caused to expand in an axial direction, but, because of the rigidity of the spacing between the emitter disc 2 and the perforated disc 9, the only motion of which the cathode tube I is capable in an axial direction is toward the open end of the cathode tube I and consequently the lugs I3 and the attached spring members I4 are moved downward by the expansion of the cathode tube I. If, during the operation of my tube, the voltage applied between the wires 6 is allowed to vary the only motion existing in the cathode assembly will be absorbed by the spring members I4 and the relation between the emitter disc 2 and the perforated disc 9 will remain substantially unchanged.

It is apparent that the spring members I4 in Figure 1 are not necessarily mounted as shown. For example, the same compressive effect in the ring II may be caused by making the spring members I4 rigid members, and forming the control element support wires I as spring members capable of drawing the control element downward against the emitter disc 2. Furthermore, the spring members I4 in Figure 1 may be eliminated completely by supporting the emitter disc 2 by a pair of insulating rings similar to the rings 29 and 30 and the metal ring 3 I, all in Figure 4.

Figure 2 represents a modified form of insulating ring which I have found to have certain advantages when used in conjunction with the embodiment of my invention shown in Figure l. The ring in Figure 2 has been modified by counterboring the surface I6 which rests against the perforated disc 9 in such a way that the path available for the conduction of heat between the emitter disc 2 and the perforated disc 9 is appreciably lengthened and the portion of the surface I6 which is in contact with the perforated disc 9 is reduced to the area II, thus the amount of cooling which the ring I I effects upon the emitter disc 2 by conducting heat to the perforated disc 9 is appreciably reduced in the modified ring I8.

A further modification of my invention is represented in Figure 3 in which the cathode tube I9 is closed at the upper end by the metal disc 20 which is coated with electron emitting substance 3. The cathode tube I9 is adapted to be heated by the heating element 4 mounted inside the tube I9 and supported upon the lead-in wires 6 by the terminal wires 5. A small portion 2| of the length of the cathode tube I9 at its lower end is spun outwardly to meet a corresponding inwardly spun portion 22 of a metal tube 23 made of a material having the same coefficient of linear expansion as that of the tube I9. The tube I9 is rigidly fastened to the tube 23 by welding or other type of fastening at the adjacent surfaces of the spun portions 2| and 22 to form the joint 26. The tube 23 is mounted at its upper end by the lugs 24 to the support wires 25.

The perforated disc 9 is carried in a Cylindrical member which is mounted on suitable support wires in a manner similar to that described in the preceding embodiment of my invention.

In operation the tubes I9 and 23 are heated by the heating element 4 and, being at substantially equal temperatures as a result of the radiation from the tube I 9 and the conduction through the joint 26, will undergo substantially equal linear expansions. Since the outer tube 23 is supported rigidly at the lugs 24 it will expand so as to move the junction 26 downward, and would thereby carry the tube I9 and its emitter surface 3 away from the aperture I 0 were it not for a similar expansion of the tube I9 in a direction upward from the junction 26. This latter expansion, however, which is equal and in a direction opposite to that of the outer tube 23, will return the emitting surface 3 to its original position, and that position will be maintained relative to the aperture I0 regardless of any variations in the voltage applied to the terminals 6 and the consequent variations of the temperature of the heater 4.

It is apparent that several modifications of this embodiment of my invention are possible. For example, the outer tube 23 may be replaced by a similar tube of shorter length of a material having a higher coefficient of linear expansion than that of tube I9 so that at equal temperatures the shorter length of the tube 23 will expand a total amount equal to the expansion of the longer tube I9. Similarly the spacing between the inner tube I9 and the outer tube 23 may be increased so that the operating temperature of the outer tube 23 is substantially lower than that of the inner tube I9 and in this case the coefiicient of expansion of the outer tube will be such that it will at its lower temperature expand an amount equal to the expansion of the inner tube I9 at its higher temperature. Thus it is apparent that the principle of compensating expansion may be applied to the mounting of an electron emitting cathode with respect to a control element in a number of ways.

A further modification of my invention employing the principle of compensating expansion is represented in Figure 4 in which a similar inner tube I9 has one end closed by a metal disc 2U on which is placed an emitting coating 3. The inner tube I9 by means of an outwardly spun portion 2lA is fastened at 26 to an inwardly spun portion 22 of an outer tube 2'I having its upper portion 28 spun outward substantially at right angles to the axis of the tube. The cathode assembly comprising the inner tube I9 and the outer tube 2l is rigidly mounted to the perforated disc 9 by supporting the flange 28 between the insulating rings 29 and 30 which are in turn held by the metal retainer 3| welded or otherwise fastened to the perforated disc 9, In order to establish electrical contact with the cathode, one end of a exible wire 32 is fastened to the ear 33 on the outer tube 21 and the other end of the wire 32 is fastened to the lead-in wire 34.

The operation of this embodiment of my invention is similar to that described in connection with Figure 3 but in this case the spacing between the emitter 3 and the aperture l0 may be more accurately adjusted in the construction of the tube by virtue of the accuracy with which the insulating ring 23 may be machined to the proper thickness.

Considering my present invention in one of its.

broader aspects, it will be seen from the foregoing that it resides in a novel method of operating cathode ray tubes for television reception wherein variations which occur in the temperature of the source of electron-emission, incidental to the development of the electron ray, are utilized to maintain substantially constant the spacing between the cathode and the control electrode. For example, in Figures 3 and 4, occurring variations in temperature of the heating element 4 are utilized to cause expansion and contraction of the metal tubes 23 and 21 to compensate for the corresponding expansion and contraction of the cathode tube I9, whereby there is maintained constant a given relative position or spacing of the point or aperture l0, at` which control of the ray intensity takes place, with respect to the point or electron-emitting substance 3 from which the ray of electrons is developed. In other words, there is utilization of the occurring variations in temperature referred to, and which heretofore have caused objectionable variations in the spacing between the control electrode and the source cf electron emission, in being simultaneously effective to bring about a compensating change whereby this spacing is actually maintained substantially constant.

. I claim:

1. A cathode ray tube including a thermally expansive electron emitter, a beam intensity ccntrol-element, and spacing means for maintaining a xed separation between said emitter and said control-element, said spacing means including thermally responsive means for compensating for thermal variation of the axial dimension of said spacing means.

2. In a cathode ray tube, a beam intensity control-element, an electron emitter, an insulating spacer between said control-element and said emitter, and means for maintaining said insulating spacer in compression, said means comprisin'g a spring member connected between said emitter and said control element.

3. In a cathode ray tube, a supporting stem, a beam intensity control-element, rigid supporting means between said control-element and said stem, an electron emissive cathode, rigid support means on said stem whereby said cathode is supported, and means for attaching said cathode to said cathode support means, said attaching means being in heat conductive communication with said cathode and comprising oppositely expansive linkages whereby the space relation between said contrcl-element and said cathode is maintained substantially independent of the temperature of said cathode.

fl. In a cathode ray tube, a supporting stern, a beam intensity control-element, rigid supporting means between said control-element and said stem, an electron emissive cathode comprising a disc-shaped electron emitter, a metal tube attached to said emitter and extending axially toward said stem, means for heating said metal tube, a second metal tubevlarger than and surrounding said rst tube and attached to said rst tube at the end of said rst tube remote from said electron emitter, said second tube ex tending in an axial direction away from said stem, a rigid support member attached to said stem whereby said cathode is supported, said larger tube being attached to said support mernber at the end of said large tube remote from the junction between said first tube and said porting said member and comprising a metallic tube disposed with its axisperpendicular to the plane of said disc, and a heating element disposed in said tube, the end of said tube adjacent said disc bearing a xed mechanical relation with respect thereto, the remaining portion of said tube being free to expand and contract only from said iirst-named end thereof in accordance .with occurring Variations in temperature of said heating element.

6. In a cathode ray tube, an electron gun including an electron emissive disc disposed in a plane substantially normal to the axis of said gun, a beam intensity control element axially disposed with respect to said electron emissive disc, and support means for maintaining a substantially constant axial juxtaposition between said electron emissive disc and said control element independently of the temperature of said emitter.

JOHN C. BATCI-IELOR. 

